Reconstructing the role of CO2 in climate change throughout the Cenozoic Step 1: The mid-Pleistocene transition

DESCRIPTION: This grant funded the study of potential pCO2 changes across the mid-Pleistocene transition, using boron isotopes in planktic foraminifers. The scope of the proposal was expanded to allow employment of a postdoc to reconstruct the boron isotopic composition of seawater throughout the Cenozoic, using epibenthic foraminifers.

OUTCOMES: The major finding of this study is that atmospheric pCO2 was relatively stable since before the mid-Pleistocene climate transition. Glacial pCO2 was ~31 µatm higher before the transition (>1 Ma) but interglacial pCO2 was similar to that of late Pleistocene interglacials (<450 ka). These estimates are consistent with a close linkage between atmospheric CO2 concentration and global climate, but the lack of a gradual decrease in interglacial pCO2 does not support the suggestion that a long-term draw down of atmospheric CO2 was the main cause of the climate transition. The deep sea benthic foraminifera data reflect a Cenozoic profile similar to the modeling study of Lemarchand et al. (Nature, 2000), with increasing δ11B from the Paleocene to the early Miocene, lower values during the Miocene, followed by an increase towards modern δ11B of seawater of 39.6 permil. Taken at face value and ignoring a potential influence of Cenozoic deep ocean pH changes, δ11B of seawater was ~2 permil lower than modern during the Miocene and ~4 permil lower than modern during the Paleocene.